The present invention relates to vehicles for travelling along conduits having fluid flowing therein, and relates particularly, but not exclusively, to vehicles for travelling along liquid transportation pipelines having liquid flowing therein.
In many industries, it is important to be able to gain access to pipelines for maintenance and/or inspection. Pipeline inspection vehicles are known which engage the internal surface of a pipeline and propel themselves along the pipeline, deriving power from a remote power source connected to the vehicle by means of an umbilical cable.
Such known pipeline inspection vehicles are generally only used for pipelines in which no fluid is flowing and if the distance to be travelled is relatively short (up to 1 km). If fluid is present and flowing it is possible to use a pig which uses the pressure of the fluid acting over sealing cups to propel the vehicle forward, that is, with the flow of the fluid. However, most conventional pigs are only uni-directional and, as such, must be recovered via a pig receiving trap at the opposite end of the pipeline. If a pig receiving trap is not fitted, which is often the case, then it is desirable to have a bi-directional vehicle. Such long range bi-directional vehicles do not presently exist. As a result of this drawback, it is usually necessary to suspend operation of the pipeline for the duration of the vehicle operation. In the case of industries such as the oil or petroleum industry, ceasing operation of a pipeline for the duration of a maintenance and/or inspection operation can involve unacceptably high cost.
Preferred embodiments of the present invention seek to overcome the above disadvantages of the prior art.
According to the present invention, there is provided a vehicle for travelling along a conduit having fluid flowing therein, the vehicle comprising:
(a) propulsion means including first surface engaging means for engaging a surface of the conduit to apply a gripping force thereto, and at least one second surface engaging means located forwardly in use of said first surface engaging means and adapted to engage a surface of the conduit to apply a gripping force thereto and adapted to move towards and away from said first surface engaging means, wherein the or each said second surface engaging means in use applies a greater gripping force when it is moving towards said first surface engaging means than when it is moving away from said first surface engaging means, and said first surface engaging means applies a larger gripping force when it is moving away from the or each said second surface engaging means than when it is moving towards the or each said second surface engaging means, to cause said propulsion means to move along the conduit;
(b) drive means having a shaft portion adapted to be rotated as a result of fluid flow relative to the drive means; and
(c) connector means for causing the or each said second surface engaging means to move away from said first surface engaging means as a result of rotation of said shaft portion.
The present invention is based on the surprising discovery that sufficient energy can be generated from the fluid flow relative to the vehicle to propel the vehicle along the conduit in the opposite direction to the direction of fluid flow. This provides the advantage that the vehicle can under certain circumstances access previously inaccessible conduits, and can crawl xe2x80x9coutwardsxe2x80x9d from a launching point against the flow of fluid and swim back an almost infinite distance to its launching point with the flow of fluid, and transport of fluid along the conduit does not need to be suspended while the vehicle is in operation. In the case of the oil and petroleum industries, this avoids the unacceptably high cost of shutting a pipeline down.
Preferably, said first and/or second surface engaging means comprises a respective plurality of resilient bristles.
By providing bristles such that the external diameter of the vehicle at the bristles is greater than the internal diameter of the conduit, the bristles can engage the internal surface of the conduit oriented in the opposite direction to the direction of travel of the vehicle. This enables the frictional force between the bristles and the conduit to be greater in one direction than in the other. This provides the further advantage that no further energy input is required to cause the bristles to apply a gripping force to the surface of the conduit, and enables the propulsion means to be constructed in a simple and cost effective manner.
Alternatively, the first and/or second surface engaging means may comprise a respective electrically and/or magnetically operated gripping means.
In a preferred embodiment, said first and/or second surface engaging means is mounted to a respective vehicle body portion and adjacent pairs of said body portions are adapted to move relative to each other.
In an alternative embodiment, said first and/or second surface engaging means is mounted to a single vehicle body portion.
The drive means may comprise at least one turbine.
At least one said turbine may be a multi stage turbine.
This provides the advantage of increasing the efficiency with which rotational energy of the shaft portion is derived from fluid flow relative to the drive means.
The drive means preferably further comprises at least one stator for altering direction of fluid flow to increase efficiency of transfer of energy from the fluid to at least one said turbine.
For example, the or each said stator may alter the direction of fluid flow to maximise the extent to which fluid contacts blades of at least one said turbine substantially perpendicularly to the face of the blades to maximise efficiency of energy transfer.
In a preferred embodiment, said connector means comprises a first part having at least one first cam groove and a second part having at least one cam projection adapted to engage at least one said first cam groove such that rotation of said shaft portion in a first sense causes at least one said cam projection to move along a said first cam groove to cause at least one said second surface engaging means to move away from said first surface engaging means.
This feature is based on the highly surprising discovery that contrary to expectations, by providing a first part having at least one first cam groove and a second part having at least one cam projection, sufficient energy can be derived from rotation of the shaft portion to cause at least one said second surface engaging means to move away from the first surface engaging means.
The first part may further include at least one second cam groove to cause at least one said second surface engaging means to move towards said first surface engaging means.
In a preferred embodiment, the or each said first cam groove has a smaller pitch than the or each said second cam groove.
Since movement of the or each said second surface engaging means away from said first surface engaging means requires more energy than movement towards said first surface engaging means (because movement of the first and second surface engaging means away from each other generally involves moving the second surface engaging means, drive means and connector means against the flow of fluid, whereas movement of the surface engaging means together generally only involves movement of the first surface engaging means against the flow of fluid), by providing the or each said second cam groove of larger pitch than the or each said first cam groove, this provides the advantage of enabling the or each second surface engaging means to be moved towards the first surface engaging means as rapidly as possible.
In a preferred embodiment, at least one said first cam groove is connected to at least one said second cam groove, and at least one said cam projection is adapted to transfer between said first and second cam grooves to reverse the direction of travel of the first part relative to the second part.
The vehicle may further comprise biasing means for urging at least one said second surface engaging means towards said first surface engaging means.
This provides the advantage that the propulsion means can under certain circumstances be constructed in a relatively simple manner, without the need for the connector means to cause the or each second surface engaging means to move towards said first surface engaging means.
The vehicle may further comprise at least one gearbox connected between said drive means and said connector means.
This provides the advantage of giving a mechanical advantage which enables the vehicle to travel more efficiently along the conduit.
In a preferred embodiment, the vehicle is articulated.
This provides the advantage of enabling the vehicle to negotiate bends in the conduit.
The vehicle is preferably articulated rearwardly of said drive means in use.
The vehicle preferably further comprises braking means for increasing the fluid drag of the vehicle.
This provides the advantage of enabling the vehicle to travel with the flow of fluid along the conduit when the vehicle is to be recovered from the conduit.
The braking means preferably comprises at least one sealing means for sealingly engaging the internal surface of the conduit.
The vehicle may further comprise one or more wheels for engaging the surface of the conduit.
The vehicle may further comprise conduit inspection means.
The vehicle may further comprise conduit repair means.